Navigation device and control method for displaying detour

ABSTRACT

The navigation device includes a detour exploring portion configured to explore a detour to avoid a section in which a traffic hazard occurs using map data at a level lower than a predetermined level when a traffic hazard determining portion determines that the traffic hazard occurs on the guidance route, and a display control portion configured to zoom the detour to match a scale of the detour to a currently designated scale, and synthesize and display the detour on a map image. The navigation device maintains the display of the wide area map and synthesizes and additionally displays a detour, for example, to pass through a road such as a narrow street included in a detailed map on the map image such that the user can receive, at a glance, a detour to easily bypass the section in which a traffic hazard occurs.

RELATED APPLICATION

The present application claims priority to Japanese Application Number2012-183834, filed Aug. 23, 2012, the entirety of which is herebyincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a navigation device and a controlmethod for displaying a detour and, in particular, to a navigationdevice and a control method for displaying a detour when a traffichazard, for example, a traffic jam occurs on a guidance route.

2. Description of the Related Art

A car-mounted navigation device generally detects a current location ofthe vehicle using an autonomous navigation sensor, a Global PositioningSystem (GPS) receiver, or the like and reads map data near the locationfrom a storage medium to display a map on a screen. Then, a driver'slocation mark that shows the vehicle location is also superimposed anddisplayed at a predetermined point on the screen such that the locationwhere the vehicle currently runs can be found at a glance.

Further, the navigation device includes a route guidance function. Theroute guidance function automatically explores a lowest-cost routeconnecting the current location to the destination using the map dataand draws the explored route as a guidance route on the map screen witha different color from the other routes and with a thick line. Further,when the vehicle approaches a point within a predetermined distance froman intersection to which the vehicle is guided on the guidance route,the device displays an enlarged map of the intersection to show theinformation about the intersection in such a way as to guide the driverto a destination.

Further, most of navigation devices include a traffic informationproviding function. The navigation device can receive the road trafficinformation sent from a road traffic information center and display thechanging road condition on the screen using the traffic informationproviding function. A navigation device including such a trafficinformation providing function can provide a user with the road trafficinformation including the information about a traffic jam or theinformation about a regulation in real time.

Some of the navigation devices including such route guidance functionand traffic information providing function also include a function forautomatically exploring a detour to avoid a traffic jam according to thereceived road traffic information (see JP 09-042984 A and JP 2006-275729A, for example). The technique disclosed in JP 09-042984 A is configuredto explore an available detour from the intersection to which thevehicle is guided on the guidance route and display the detour when thevehicle approaches the intersection to which the vehicle is guided. Thetechnique disclosed in JP 2006-275729 A is configured to storeinformation about the frequently-used shortcuts and back roads in themap data to selectively extract only the shortcut or the back road to goalong the guidance route toward the destination from among the shortcutsand back roads and display the extracted shortcut or back road on thescreen.

Map data used for a navigation device is generally layered in unitsreferred to as levels and managed. The levels include a higher level atwhich a map shows a panoramic view of a wide area, and a lower level atwhich a map depicts the detail of a narrow area. The map data at one ofthe layers is read according to the scale designated by the user andthen a map is displayed on the screen based on the map data. The smallerscale the wide area map is on, the fewer the elements (roads, icons orthe like) are displayed on the map. The larger scale the detailed map ison, the more the elements are displayed on the map.

Accordingly, there is a problem in that a road that is not included inthe map data at the level corresponding to the currently designatedscale (currently displayed on the screen) cannot be displayed as adetour even if a detour is explored near the intersection to which thevehicle is guided as described in JP 09-042984 A. Similarly, there is aproblem in that a road that is not included in the map data at the levelcorresponding to the currently designated scale cannot be displayed as ashortcut or a back road even if a shortcut or a back road is displayedas described in JP 2006-275729 A.

There is a problem in that, if it is desirable that narrow roads such asa narrow street are displayed as detours, shortcuts or back roads, it isnecessary to change the designation of the scale to a level at which thedetailed map of the city is displayed, and this complicates theoperation. Further, there is a problem in that, if the scale isincreased to a level at which the detailed map of the city is displayed,it is difficult to see an overview the detour, the shortcut, or the backroad. This brings a feeling of anxiety to the driver because it isdifficult for the driver to know the route of the detour or how far isthe detour. A road having a width of less than 5.5 m is referred to as anarrow street in Japan. The narrow street corresponds to a road referredto as a minor street or a secondary street in the United States.

SUMMARY

In light of the foregoing, an objective of the present invention is toshow the user a detour to avoid a traffic hazard, for example, a trafficjam, in an easily understood manner without an operation for changingthe scale to be larger, even if the small-scale wide area map iscurrently displayed.

To solve the above-mentioned problems, according to the presentinvention, map data at a level lower than a predetermined level is usedfor exploring a detour for avoiding a section in which a traffic hazardoccurs when the occurrence of the traffic hazard on the guidance routeis detected. Then, the image of the explored detour is synthesized anddisplayed on the map image on the currently designated scale while beingzoomed in order to match the scale of the image to the currentlydesignated scale.

According to the present invention having the above-mentionedconfiguration, while a small-scale wide area map is displayed, thedisplay of the wide area map is maintained and a detour to pass througha road included in a detailed map showed using map data at a level lowerthan a predetermined level is synthesized and additionally displayed.The detour is synthesized and displayed on the wide area map while theroutes included in the detailed map are zoomed. This can display thedetour over a wide area. Thus, the user can receive an overview of thedetour. Thus, according to the present invention, a detour to avoid atraffic hazard, for example, a traffic jam, can be shown to the user inan easily understood manner without a user's complicated operation forchanging the scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of the functional configurationof a navigation device according to an embodiment;

FIGS. 2A and 2B are views of exemplary navigation images displayed usinga display control portion according to an embodiment;

FIG. 3 is a flowchart for describing an exemplary operation of thenavigation device according to an embodiment; and

FIG. 4 is a block diagram for illustrating another example of thefunctional configuration of the navigation device according to anembodiment.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will be describedbased on the drawings. FIG. 1 is a block diagram of an example of thefunctional configuration of a navigation device 100 in the presentembodiment. As illustrated in FIG. 1, the navigation device 100according to the present embodiment includes, as its functionalcomponents, a map data storing portion 1, a reading control portion 2, amap data memory 3, a current location measuring device 4, a beacontransceiver 5, a destination setting portion 6, a guidance routeexploring portion 7, a guidance route memory 8, a traffic hazarddetermining portion 9, a detour exploring portion 10, a detour memory11, and a display control portion 12. Further, the display controlportion 12 includes, as its specific functional components, a mapdrawing portion 12 a, a guidance route drawing portion 12 b, a detourdrawing portion 12 c, and an image synthesizing portion 12 d.

Note that each function of the reading control portion 2, thedestination setting portion 6, the guidance route exploring portion 7,the traffic hazard determining portion 9, the detour exploring portion10, and the display control portion 12 can be implemented by any ofhardware, a Digital Signal Processor (DSP), and software. For example,when being implemented by software, each of the above-mentionedfunctions may include a CPU, an MPU, a RAM, a ROM, and the like that areincluded in the navigation device 100, and implementation may be by anexecution of the program stored in the RAM or the ROM.

A hard disk, a semiconductor memory, or the like can be used as arecording medium for recording the above-mentioned program in additionto the RAM and the ROM. Further, the above-mentioned program can bedownloaded to the navigation device 100 through a network, for example,the Internet.

The map data storing portion 1 is for storing map data necessary todisplay a map or explore a route and, for example, includes a hard disk.Note that a DVD, a CD-ROM, a semiconductor memory, or the like can beused as a recording medium included in the map data storing portion 1 inaddition to the hard disk.

The map data recorded in the map data storing portion 1 is layered inunits referred to as levels and managed. The levels include a higherlevel at which a map shows a panoramic view of a wide area, and a lowerlevel at which a map depicts the detail of a narrow area. The map dataat each of the levels includes various types of drawing data necessaryto display a map, and road data necessary for various processes such asmap matching, route exploring, or route guiding.

The higher the level of the map data that covers a wide area, thesmaller the number of the roads that are included in the road data. Inother words, the map data at a higher level primarily includes only theroad data about main roads, and does not include the data about minorroads, such as narrow streets. On the other hand, the lower the level ofthe map data that shows the detailed narrow area, the larger the numberof the roads that are included in the road data. In other words, the mapdata at a lower level includes a lot of data about minor roads, such asnarrow streets.

The reading control portion 2 controls the process for reading the mapdata from the map data storing portion 1 and temporarily storing the mapdata in the map data memory 3. When a map around the current location ofa vehicle is displayed on a display device 200, the reading controlportion 2 inputs the information about the vehicle's current locationfrom the current location measuring device 4 to read, from the map datastoring portion 1, the map data within a predetermined range, includingthe vehicle's current location, and stores the map data in the map datamemory 3.

On the other hand, when a guidance route is explored, the readingcontrol portion 2 reads, from the map data storing portion 1, the mapdata within a predetermined range, including the range from thevehicle's current location to the destination, and stores the map datain the map data memory 3. Further, when a detour is explored, thereading control portion 2 reads, from the map data storing portion 1,the map data within a predetermined range, including the range from thevehicle's current location to the end of the detour (to be described indetail below), and stores the map data in the map data memory 3.

The current location measuring device 4 is for measuring the currentlocation of the vehicle, and includes an autonomous navigation sensor, aGPS transceiver, a location calculating CPU, and the like. Theautonomous navigation sensor includes a vehicle speed sensor (distancesensor) configured to output a pulse at predetermined intervals of thetravel distance in order to detect the travel distance of the vehicle,and an angular velocity sensor (relative bearing sensor), for example, avibrating gyro configured to detect the rotation angle of the vehicle(travel bearing). The autonomous navigation sensor detects the relativelocation and bearing of the vehicle using the vehicle speed sensor andthe angular velocity sensor.

The location calculating CPU calculates the absolute location of theuser's vehicle (estimated vehicle location) and the vehicle bearingbased on the data of the relative location and bearing of the user'svehicle output from the autonomous navigation sensor. Further, the GPStransceiver receives the radio waves sent from a plurality of GPSsatellites with a GPS antenna in order to calculate the absolutelocation and bearing of the vehicle by a three-dimensional positioningprocess or a two-dimensional positioning process (the vehicle bearing iscalculated based on the user's vehicle current location and the user'svehicle location before a sampling time ΔT).

The beacon transceiver 5 bilaterally communicates with a radio wavebeacon transceiver mainly placed on an expressway via radio waves andbilaterally communicates with an optical beacon transceiver mainlyplaced on a public road via lights in order to receive the road trafficinformation sent from a road traffic information center (notillustrated). The road traffic information includes the informationindicating a road section in which a traffic hazard occurs due to atraffic jam, a construction, or the like.

The destination setting portion 6 sets a destination of the guidanceroute in response to a user operation of an operation portion (notillustrated). The guidance route exploring portion 7 explores alowest-cost guidance route connecting the vehicle's current locationthat has been measured with the current location measuring device 4 toits destination that has been set with the destination setting portion 6using the map data stored in the map data memory 3. The guidance routememory 8 temporarily stores the data about the guidance route exploredwith the guidance route exploring portion 7.

The traffic hazard determining portion 9 determines whether a traffichazard occurs on the guidance route ahead of the current location basedon the vehicle's current location that has been measured with thecurrent location measuring device 4, the data about the guidance routestored in the guidance route memory 8, and the road traffic informationreceived with the beacon transceiver 5.

When the traffic hazard determining portion 9 determines that a traffichazard occurs, the detour exploring portion 10 explores a detour toavoid the section on the guidance route in which the traffic hazardoccurs using the map data stored in the map data memory 3 and the dataabout the guidance route stored in the guidance route memory 8. At thattime, the detour exploring portion 10 uses the map data at a level lowerthan a predetermined level in order to explore a detour. In that case,the map data at a predetermined level means the map data storing roadnetwork data, except for narrow streets. The map data at a level lowerthan the predetermined level means the map data storing road networkdata, including narrow streets. The navigation device 100 sets whichlevel of the map data is to be used.

The detour exploring portion 10 determines whether the vehicle hasreached a point at a predetermined distance from the beginning of thesection on the guidance route in which the traffic hazard occurs, forexample, based on the vehicle current location measured with the currentlocation measuring device 4. When the vehicle has reached the point, thedetour exploring portion 10 explores a detour. Alternatively, when thevehicle has reached the intersection at a predetermined distance fromthe beginning of the section on the guidance route in which the traffichazard occurs (more specifically, a point at a predetermined distancefrom the intersection), the detour exploring portion 10 can explore adetour.

When exploring a detour, the detour exploring portion 10 provisionallysets the end of the detour in order to explore a low-cost detourconnecting the current location to the end of the detour. At that time,the detour exploring portion 10 sets a high cost to the section on theguidance route in which the traffic hazard occurs in order to avoidexploring the section as a part of the detour. At that time, the end ofthe detour, for example, is a point on the guidance route and anintersection next to the end of the section in which the traffic hazardoccurs (on the destination side).

In the present embodiment, a detour or a plurality of detours can beexplored. Hereinafter, the embodiment will be described on theassumption that a plurality of detours is explored. When exploring aplurality of detours, the detour exploring portion 10 can explore apredetermined number of the detours in order of increasing the cost.Alternatively, the detour exploring portion 10 can explore thelowest-cost detour from among the detours avoiding the section in whichthe traffic hazard occurs and also can explore another detour connectingto the lowest-cost detour in order to explore a plurality of detours.

The detour memory 11 temporarily stores the data about the detourexplored with the detour exploring portion 10. In the presentembodiment, the detour exploring portion 10 explores a plurality ofdetours. Accordingly, the data about a plurality of the detours exploredwith the detour exploring portion 10 are stored in the detour memory 11.

The display control portion 12 controls the display of the navigationimage on the display device 200. To perform the display control, thedisplay control portion 12 includes the map drawing portion 12 a, theguidance route drawing portion 12 b, the detour drawing portion 12 c,and the image synthesizing portion 12 d.

The map drawing portion 12 a draws a map image necessary for the displayon the display device 200 based on the map data temporarily stored inthe map data memory 3. At that time, the map drawing portion 12 a drawsthe map image around the user's vehicle location according to the scaledesignated by the user and using the map data at a level correspondingto the scale. Note that, when the map data at a level corresponding tothe currently designated scale is not included, the map drawing portion12 a performs digital zooming using the map data at a level near thescale in order to draw the map image around the user's vehicle location.Then, the map drawing portion 12 a outputs a screen of the drawn mapimage to the image synthesizing portion 12 d.

The guidance route drawing portion 12 b draws the guidance route imagebased on the guidance route data stored in the guidance route memory 8.In other words, the guidance route drawing portion 12 b selectivelyreads the data included in a screen of the map area currently outputfrom the map drawing portion 12 a to the image synthesizing portion 12 dfrom among the guidance route data stored in the guidance route memory8. Then, the guidance route drawing portion 12 b draws the guidanceroute using the read guidance route data while emphasizing the guidanceroute with a predetermined color and with a thick line, and outputs theguidance route to the image synthesizing portion 12 d.

The detour drawing portion 12 c draws a detour image based on the detourdata stored in the detour memory 11. As described above, the detourmemory 11 stores the detour data about a plurality of detours.Accordingly, the detour drawing portion 12 c draws a plurality of thedetour images based on the data about the detours stored in the detourmemory 11, respectively.

At that time, the detour drawing portion 12 c selectively reads the dataincluded in a screen of the map area currently output from the mapdrawing portion 12 a to the image synthesizing portion 12 d from amongthe detour data stored in the detour memory 11. Then, the detour drawingportion 12 c draws the detour in a display form different from a roadincluded in the map image on the designated scale using the read detourdata in order to output the detour to the image synthesizing portion 12d. For example, the map drawing portion 12 a draws a detour whilehighlighting the detour with a predetermined color different from theroads and guidance route included in the map image on the designatedscale.

The image synthesizing portion 12 d synthesizes various images andoutputs the images to the display device 200. When a guidance route hasbeen set, the image synthesizing portion 12 d superimposes the guidanceroute image drawn with the guidance route drawing portion 12 b on themap image drawn with the map drawing portion 12 a in order to synthesizethe images, and then outputs the result of the synthesis to the displaydevice 200. This displays the information about the map around theuser's vehicle location together with the guidance route on the screenof the display device 200.

When a detour is explored while the vehicle runs after a guidance routehas been set, the image synthesizing portion 12 d superimposes theguidance route image drawn with the guidance route drawing portion 12 band the detour image drawn with the detour memory 11 on the map imagedrawn with the map drawing portion 12 a in order to synthesize theimages, and then outputs the result from the synthesis to the displaydevice 200. This displays the information about the map around theuser's vehicle location together with the guidance route and the detouron the screen of the display device 200.

In the present embodiment, the map drawing portion 12 a draws a mapimage according to the currently designated scale. On the other hand,the detour exploring portion 10 explores a detour using the map data ata lower level including narrow streets regardless of the currentlydesignated scale and the detour drawing portion 12 c draws the detourimage using the explored detour data. Thus, the scale of the map imagesometimes differs from the scale of the detour image when the detourimage is superimposed on the map image to synthesize the images. Inlight of the foregoing, the image synthesizing portion 12 d zooms outfrom the detour image drawn with the detour drawing portion 12 c inorder to match the scale of the detour image to the currently designatedscale (the scale of the map image) and synthesizes the detour image withthe map image.

At that time, in the present embodiment, the display of the guidanceroute is not erased to display a detour when the detour has beenexplored, but the display of the guidance route is maintained toadditionally synthesize and display the detour. At that time, todistinguish the guidance route from the detour at a glance, the detouris displayed in a display form different from the guidance route. Inother words, in the present embodiment, the detour is not exploredinstead of the original guidance route and is not placed as a newguidance route, but the display of the original guidance route as theguidance route is maintained and the detour is separately displayed in aform easy to understand at a glance.

Further, in the present embodiment, only the detour explored by thedetour exploring portion 10 is synthesized and is displayed on the mapimage from among the roads included in the map data at a level lowerthan the predetermined level used when the detour has been explored.Although a lot of roads, such as a narrow street, are included in themap data at a lower level, displaying all of the roads complicates thescreen. This makes it difficult for the user to instantaneouslyrecognize which part is the detour. On the other hand, as in the presentembodiment, synthesizing and displaying only the explored detour on themap image enables the user to instantaneously recognize the detour.

FIGS. 2A and 2B are views of exemplary navigation images displayed withthe display control portion 12. FIG. 2A illustrates a state in whichonly a guidance route 20 is synthesized and displayed on the map imagewithout the occurrence of a traffic hazard on the guidance route. On theother hand, FIG. 2B illustrates a state in which detours 22 to avoid asection in which the traffic hazard occurs are explored and aresynthesized and displayed on the map image together with the guidanceroute 20 because the traffic hazard (traffic jam) occurs on the guidanceroute 20 as described with a reference sign 21.

In the example in FIG. 2B, when the vehicle reaches a point (currentlocation) 24 at a predetermined distance from a beginning 23 of thesection on the guidance route 20 in which the traffic hazard occurs, anintersection next to the end of the section in which the traffic hazardoccurs and on the guidance route 20 has provisionally been set as adetour end 25, and three detours 22 that connect the current location 24to the detour end 25 at low cost have been explored. Then, the threedetours 22 are displayed in a form distinguishable from the guidanceroute 20 and the other roads without changing the scale currentlydesignated in the current map image.

FIG. 3 is a flowchart of an exemplary operation of the navigation device100 having the configuration as described above and according to thepresent embodiment. Note that the process of the flowchart illustratedin FIG. 3 is started when the vehicle starts running after a guidanceroute has been set. First, the traffic hazard determining portion 9determines based on the road traffic information received with thebeacon transceiver 5 whether a traffic hazard occurs on the guidanceroute (step S1).

When it is determined that a traffic hazard does not occur on theguidance route, the procedure in step S1 is continued. On the otherhand, when it is determined that a traffic hazard occurs on the guidanceroute, the detour exploring portion 10 determines based on the vehiclecurrent location measured with the current location measuring device 4whether the vehicle has been reached a point at a predetermined distancefrom the beginning of the section in which the traffic hazard occurs onthe guidance route (step S2).

When it is determined that the vehicle has not yet reached the point ata predetermined distance from the beginning of the section in which thetraffic hazard occurs, the procedure in step S2 is continued. On theother hand, when it is determined that the vehicle has reached the pointat a predetermined distance from the beginning of the section in whichthe traffic hazard occurs, the detour exploring portion 10 explores adetour to avoid the section in which the traffic hazard occurs using themap data at a level lower than a predetermined level (step S3).

The display control portion 12 zooms out from the detour explored withthe detour exploring portion 10 in order to match the scale of thedetour to the currently designated scale, and synthesizes and displaysthe detour on the map image on the currently designated scale togetherwith the guidance route (step S4). After that, the display controlportion 12 determines based on the vehicle current location measuredwith the current location measuring device 4 whether the vehicle hasbypassed the section in which the traffic hazard occurs to thedestination side (step S5).

When it is determined that the vehicle has not bypassed yet the sectionin which the traffic hazard occurs, the process goes back to step S4. Onthe other hand, when it is determined that the vehicle has bypassed thesection in which the traffic hazard occurs, the display control portion12 erases the synthesized and displayed detour from the navigation image(step S6).

After that, the traffic hazard determining portion 9 determines based onthe vehicle's current location measured with the current locationmeasuring device 4 and the data about the guidance route stored in theguidance route memory 8 whether the vehicle has reached the destination(step S7). When it is determined that the vehicle has not reached thedestination yet, the process goes back to step S1. On the other hand,when it is determined that the vehicle has reached the destination, theprocess of the flowchart illustrated in FIG. 3 is terminated.

As described in detail above, in the present embodiment, when theoccurrence of a traffic hazard on the guidance route is detected, adetour to avoid the section in which the traffic hazard occurs isexplored using the map data at a level lower than a predetermined level.Then, the explored detour is zoomed out in order to match the scale ofthe detour to the currently designated scale and the detour issynthesized and displayed on the map image on the currently designatedscale.

According to the present embodiment having the above-mentionedconfiguration, while a small-scale wide area map is displayed, thedisplay of the wide area map is maintained and a detour, for example, topass through a narrow street is synthesized and additionally displayedon the map. Further, according to the present embodiment, not all of theroads included in the map data at a lower level used for exploring thedetour are synthesized and displayed, but only the explored detour issynthesized and displayed. Further, the detour is displayed in a formdistinguishable from the roads and guidance route included in the mapimage on the currently designated scale.

This enables the user to receive a detour which the user can easilybypass the section in which a traffic hazard occurs and avoid a one-wayroad, an extremely narrow road or the like at a glance, without theeffort of the operation for changing the scale to be larger in order todisplay a detailed map. Further, according to the present embodiment,the user can also receive an overview of the detour because the routesincluded in the detailed map are zoomed out in such a way to besynthesized and displayed on the wide area map and thus this can displaythe detour over the wide area. In the example illustrated in FIG. 2B,the entirety of the detours can be overviewed. Thus, the user can travelat ease along the displayed detour.

Note that the section in which the traffic hazard occurs is relativelyshort so that the section is included in a screen of the map on thecurrently designated scale in the example illustrated in FIG. 2B. Thus,the entirety of the explored detours is also displayed in the screen.However, if the section in which a traffic hazard occurs is long, thesection is not included in a screen and thus the entirety of theexplored detours is also not included in the screen. In such a case, thescale can automatically be changed such that the entirety of the sectionin which a traffic hazard occurs can be included in a screen. FIG. 4 isa view of an exemplary configuration for the above-mentioned case.

In the embodiment illustrated in FIG. 4, the configuration illustratedin FIG. 1 further includes a hazard section determining portion 41 and ascale changing portion 42. The hazard section determining portion 41determines whether the entirety of the section in which a traffic hazardoccurs is included in a screen of the map image drawn with the mapdrawing portion 12 a on the currently designated scale when the traffichazard determining portion 9 determines that the traffic hazard occurs.

The scale changing portion 42 automatically changes the scale to a scaleat which the entirety of the section in which a traffic hazard occurs isincluded in a screen when it is determined that the entirety of thesection in which a traffic hazard occurs is not included in a screen onthe currently designated scale, and then notifies the fact to the mapdrawing portion 12 a. After receiving the notification, the map drawingportion 12 a draws a map image according to the changed scale. Further,the image synthesizing portion 12 d zooms our from the detour imagedrawn with the detour drawing portion 12 c based on the detour datastored in the detour memory 11 in order to match the scale of the detourimage to the scale changed with the scale changing portion 42, andsynthesizes and displays the detour image on the map image on thechanged scale.

Note that, although it is determined in the example whether the entiretyof the section in which a traffic hazard occurs is included in a screenof the map image on the currently designated scale, the presentinvention is not limited to the determination. For example, it can bedetermined whether the entirety of the detour explored with the detourexploring portion 10 is included in a screen of the map image on thecurrently designated scale.

Further, although the example in which the detour is highlighted anddisplayed has been described in the above-mentioned embodiment, thepresent invention is not limited to the example. In other words, anyform other than the highlight display can be used as long as the form isdistinguishable from the roads and guidance route included in the mapimage on the currently designated scale.

Further, although the fact that the explored detours are displayed informs distinguishable from each other has not been mentioned in theembodiment, the explored detours can be displayed in such forms. In thatcase, the detours are preferably displayed such that it can bedetermined at a glance which detour is the smallest in cost.

Further, although the example in which a detour is explored using themap data at a preset level lower than a predetermined level regardlessof the currently designated scale has been described in theabove-mentioned embodiment, the present invention is not limited to theexample. For example, when the currently designated scale is already setat a level lower than the predetermined level, a detour can be exploredusing the map data at a level corresponding to the scale.

Further, although the example in which a level lower than apredetermined level is set to be a level at which a narrow street isincluded in the road data to the navigation device 100, the presentinvention is not limited to the example. For example, the navigationdevice 100 includes a route exploring road database including a lowerlevel storing the road network data, including a narrow street, and anupper level storing the road network data, except a narrow street. Thenavigation device 100 can refer only to the lower level while exploringa detour. Further, on the assumption that the predetermined level is alevel corresponding to the currently designated scale, a detour can beexplored using the map data at a level that is n (n is one or more)levels below the level corresponding to the currently designated scale.

Further, the above-mentioned embodiment merely describes a specificexample when the present invention is implemented. This shall not make arestrictive interpretation of the technical scope of the presentinvention. In other words, the present invention can be variouslyimplemented without departing from the gist or main feature of thepresent invention.

While there has been illustrated an described what is at presentcontemplated to be preferred embodiments of the present invention, itwill be understood by those skilled in the art that various changes andmodifications may be made, and equivalents may be substituted forelements thereof without departing from the true scope of the invention.In addition, many modifications may be made to adapt a particularsituation to the teaching of the invention without departing from thecentral scope thereof. Therefore, it is intended that this invention notbe limited to the particular embodiments disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

What is claimed is:
 1. A navigation device comprising: a traffic hazarddetermining portion configured to determine based on road trafficinformation whether a traffic hazard occurs on a guidance route; adetour exploring portion configured to explore a detour to avoid asection in which the traffic hazard occurs using map data at a levellower than a predetermined level when the traffic hazard determiningportion determines that the traffic hazard occurs; and a display controlportion configured to control displaying such that the detour exploredwith the detour exploring portion is zoomed in order to match a scale ofthe detour to a scale of a currently displayed map image designated by auser, and is synthesized and displayed on the currently displayed mapimage; wherein the detour exploring portion is configured to determinebased on a vehicle current location whether a vehicle has reached apoint on the guidance route that precedes the traffic hazard, and whenit is determined that the vehicle has reached the point, the detourexploring portion is configured to explore the detour to avoid thetraffic hazard; and, wherein the scale of the currently displayed mapimage does not change when the detour is displayed on the currentlydisplayed map image.
 2. The navigation device according to claim 1,wherein the map data at the level lower than the predetermined levelstores road network data including a narrow street.
 3. The navigationdevice according to claim 1, wherein the display control portioncontrols displaying such that only the detour explored with the detourexploring portion is synthesized and displayed from among roads includedin the map data at the level lower than the predetermined level.
 4. Thenavigation device according to claim 1, wherein the display controlportion controls displaying such that the detour is synthesized anddisplayed while a display of the guidance route is maintained.
 5. Thenavigation device according to claim 1, wherein the display controlportion controls displaying such that the detour explored with thedetour exploring portion is displayed in a display form different fromroads included in the currently displayed map image.
 6. The navigationdevice according to claim 1, wherein the detour exploring portionexplores a plurality of detours to avoid the section in which thetraffic hazard occurs, and wherein the display control portion controlsdisplaying such that the detours explored with the detour exploringportion are synthesized and displayed.
 7. The navigation deviceaccording to claim 6, wherein the detour exploring portion explores alowest-cost detour from among the detours to avoid the section in whichthe traffic hazard occurs, and explores another detour connecting to thelowest-cost detour in order to explore the detours.
 8. A control methodfor displaying a detour comprising: determining, using a traffic hazarddetermining portion of a navigation device, based on road trafficinformation, whether a traffic hazard occurs on a guidance route;exploring, using a detour exploring portion of the navigation device, adetour to avoid a section in which the traffic hazard occurs using mapdata at a level lower than a predetermined level when the traffic hazarddetermining portion determines that the traffic hazard occurs; andcontrolling, using a display control portion of the navigation device,displaying such that the detour explored with the detour exploringportion is zoomed in order to match a scale of the detour to a scale ofa currently displayed map image designated by a user, and is synthesizedand displayed on the currently displayed map image; wherein the detourexploring portion is configured to determine based on a vehicle currentlocation whether a vehicle has reached a point on the guidance routethat precedes the traffic hazard, and when it is determined that thevehicle has reached the point, the detour exploring portion isconfigured to explore the detour to avoid the traffic hazard; and,wherein the scale of the currently displayed map image does not changewhen the detour is displayed on the currently displayed map image. 9.The control method for displaying a detour according to claim 8, whereinthe map data at the level lower than the predetermined level stores roadnetwork data including a narrow street.
 10. A navigation devicecomprising: a traffic hazard determining portion configured to determinebased on road traffic information whether a traffic hazard occurs on aguidance route; a detour exploring portion configured to explore adetour to avoid a section in which the traffic hazard occurs using mapdata at a level lower than a predetermined level when the traffic hazarddetermining portion determines that the traffic hazard occurs; a displaycontrol portion configured to control displaying such that the detourexplored with the detour exploring portion is zoomed in order to match ascale of the detour to a scale of a currently displayed map imagedesignated by a user, and is synthesized and displayed on the currentlydisplayed map image; a hazard section determining portion configured todetermine whether an entirety of the section in which the traffic hazardoccurs is included in a screen of the map image currently displayed whenthe traffic hazard determining portion determines that the traffichazard occurs; and a scale changing portion configured to change thescale of the currently displayed map image to a scale at which theentirety of the section in which the traffic hazard occurs is includedin a screen when the hazard section determining portion determines thatthe entirety of the section in which the traffic hazard occurs is notincluded in the screen of the map image currently displayed, wherein thedisplay control portion controls displaying such that the detourexplored with the detour exploring portion is zoomed in order to matchthe scale of the detour to the scale changed with the scale changingportion, and is synthesized and displayed on a map at the changed scale.11. The navigation device according to claim 10, wherein the map data atthe level lower than the predetermined level stores road network dataincluding a narrow street.
 12. The navigation device according to claim10, wherein the display control portion controls displaying such thatonly the detour explored with the detour exploring portion issynthesized and displayed from among roads included in the map data atthe level lower than the predetermined level.
 13. The navigation deviceaccording to claim 10, wherein the display control portion controlsdisplaying such that the detour is synthesized and displayed while adisplay of the guidance route is maintained.
 14. The navigation deviceaccording to claim 10, wherein the display control portion controlsdisplaying such that the detour explored with the detour exploringportion is displayed in a display form different from roads included inthe currently displayed map image.
 15. The navigation device accordingto claim 10, wherein the detour exploring portion explores a pluralityof detours to avoid the section in which the traffic hazard occurs, andwherein the display control portion controls displaying such that thedetours explored with the detour exploring portion are synthesized anddisplayed.
 16. The navigation device according to claim 15, wherein thedetour exploring portion explores a lowest-cost detour from among thedetours to avoid the section in which the traffic hazard occurs, andexplores another detour connecting to the lowest-cost detour in order toexplore the detours.